In these days of high fuel costs a fuel-consummption monitor can allow the operator of a combustion engine, for instance the driver of a car, to operate the engine in the most efficient possible manner, and to keep track of the precious fuel. This can be done relatively easily in a gasoline engine by providing a flowmeter in the fuel line leading from the gas tank to the fuel pump. The meter can be set up to display the instantaneous rate of flow in units of volume per units of time, as well as the overall amount of flow in simple units of volume.
In a diesel engine, however, the problem is substantially more complex. Fuel is drawn through a feed line from the tank by means of a pump and is supplied to injectors of the diesel engine under high pressure. A return line allows fuel not injected in the engine to be returned to the tank. In order to fit out such an engine system with a fuel-consumption monitor a control arrangement is provided between the pump and the tank. The return line is fed back to this control arrangement which in turn operates the pump at such a rate as to keep the pumped amount of fuel substantially equal to the consumed amount. A flowmeter provided between this control arrangement and the tank can, therefore, give a rough figure of fuel consumption.
Such a system has the considerable disadvantage that it is quite expensive. Furthermore the device does not provide a readout of the instantaneous rate of fuel consumption. Furthermore such arrangements are normally set up so that the fuel consumption is read with some difficulty and only periodically. Therefore the devices do not allow a person to adjust his or her driving habits for greatest fuel efficiency.